<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1, user-scalable=no">
    <meta http-equiv="X-UA-Compatible" content="ie=edge,chrome=1">
    <meta name="author" content="陈嘉乐">
    <title></title>
    <style>
 .box{
width: 400px;
border: 1px solid #000;
margin: 50px auto;
 }
.tab{
    margin: 0;
    padding: 0;
    list-style: none;
    background-color: #000;
}
 li{
    width: 60px;
    float: left;
    text-align: center;
    line-height: 40px;
    color: white;
}
 .active{
    color: black;
    background-color: #aaa;
} 
p{
    display: none;
}
p:first-child{
    display: block;
}
.clearfix::after{
    content: '';
    clear: both;
    display: block;
    height: 0;
    visibility: hidden;
}


</style>
</head>
<body>
<div class="box">
    <ul class="tab clearfix">
          <li class="active">新闻</li>
    <li>公告</li>
    <li>赛程</li>
    </ul>
    <div class="content">
        <p>1--新闻<br>新闻<br>新闻<br> </p>
        <p>2--公告<br>公告<br>公告<br></p>
        <p>3--赛程<br>赛程<br>赛程<br></p>
    </div>
</div>
</body>
</html>
<script>

var lis = document.querySelectorAll('.tab li');
var allP = document.querySelectorAll('p');

for(var i = 0; i< lis.length;i++){
    lis[i].index = i;
    lis[i].onmouseover = function () {
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</script>